Is it possible to define a class constant inside an Enum?

Question

Python 3.4 introduces a new module enum, which adds an enumerated type to the language. The documentation for enum.Enum provides an example to demonstrate how i

Answer 1

A property can be used to provide most of the behaviour of a class constant:

class Planet(Enum):

    # ...

    @property
    def G(self):
        return 6.67300E-11

    # ...

    @property
    def surface_gravity(self):
        return self.G * self.mass / (self.radius * self.radius)

This would be a little unwieldy if you wanted to define a large number of constants, so you could define a helper function outside the class:

def constant(c):
    """Return a class property that returns `c`."""
    return property(lambda self: c)

... and use it as follows:

class Planet(Enum):

    # ...

    G = constant(6.67300E-11)

One limitation of this approach is that it will only work for instances of the class, and not the class itself:

>>> Planet.EARTH.G
6.673e-11
>>> Planet.G